Calling C++ class methods via a function pointer

Question

How do I obtain a function pointer for a class member function, and later call that member function with a specific object? I’d like to write:

class Dog : A         


        

Answer 1

I came here to learn how to create a function pointer (not a method pointer) from a method but none of the answers here provide a solution. Here is what I came up with:

template  struct MethodHelper;
template  struct MethodHelper {
    using T = Ret (C::*)(Args...);
    template  static Ret call(C* object, Args... args) {
        return (object->*m)(args...);
    }
};

#define METHOD_FP(m) MethodHelper::call

So for your example you would now do:

Dog dog;
using BarkFunction = void (*)(Dog*);
BarkFunction bark = METHOD_FP(&Dog::bark);
(*bark)(&dog); // or simply bark(&dog)

Edit:
Using C++17, there is an even better solution:

template  struct MethodHelper;
template  struct MethodHelper {
    static Ret call(C* object, Args... args) {
        return (object->*m)(args...);
    }
};

which can be used directly without the macro:

Dog dog;
using BarkFunction = void (*)(Dog*);
BarkFunction bark = MethodHelper<&Dog::bark>::call;
(*bark)(&dog); // or simply bark(&dog)

For methods with modifiers like const you might need some more specializations like:

template  struct MethodHelper {
    static Ret call(const C* object, Args... args) {
        return (object->*m)(args...);
    }
};